[openbeosnetteam] Re: Dial-Up

In Thu, 10 Apr 2003 10:21:32 +0200, Emmanuel Jacobs said:

> If I understand well: if you intend to do zero_copy for TCP
> transmission you should keep a sent segment in memory until the OS
> receive an TCP ack for that one.

In other words, it is not zero copy as you will have to copy the packet 
to keep it.

> Is it the management of this which is causing the overkill or is it
> more a memory usage impact ?

Well, the basic principle you base your question on is wrong. :)

> If not, where the performance issue is coming from ? (it is not very
> clear for me :-)

If you try to do a zero-copy process in this case you will have to 
recreate the packet in the case a retransmission is required. 
Recreating the packet is *WAY* more costly than doing a copy.

AFAIK, there are no zero-copy stacks available. All of them are nearly 
zero-copy (no copy on receive and one copy on transmission). 

-Bruno


--
Fortune Cookie Says:

The rain it raineth on the just
        And also on the unjust fella,
But chiefly on the just, because
        The unjust steals the just's umbrella.

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